The continuing demand for increasing computational power and memory space is driving the miniaturization of integrated circuits. To sustain progress, miniaturization will soon be driven into the nanometer regime. Unfortunately, conventional devices cannot be scaled down straightforwardly, because of problems caused by parasitic resistances, scattering and tunneling.
Single-electronics offers solutions to some of the problems arising from miniaturization. Single-electronic devices can be made from readily available materials and can use as little as one electron to define a logic state. Unlike conventional devices, single-electron devices show improved characteristics when their feature size is reduced. This follows from the fact that single-electron devices are based on quantum mechanical effects that are more pronounced at smaller dimensions. Single-electron devices also have low power consumption and therefore there are less energy restrictions to exploit the high integration densities that are possible with such devices.
The practical implementation of single-electronic devices capable of reproducibly defining a logic state remains problematic, however. For instance, it is desirable to develop process technology conducive to the mass production of nanometer scale single-electron devices structures and for such devices to operate at room temperature. Much more important than mass production and room temperature operation, however, is the sensitivity of single-electron devices towards random background charge effects.
A random background charge can alter the Coulomb blockade energy, thereby altering the operating characteristics of the device. For instance, a trapped or moving charge in proximity to a single-electron transistor (SET) logic gate could flip the device's logic state, thereby making the output from the device unreliable at any temperature. In addition, background charge movement can cause the device's characteristics to shift over time.
Previous attempts to reduce the random background charge dependence of single-electronic devices have not been entirely successful. Efforts to find impurity-free fabrication techniques have not lead to devices that are sufficiently free of random background charge. Adding redundancy into the logic circuit is considered to be ineffective, especially in the presence of high background charge noise levels. An operating-point-refresh to adjust the bias conditions of the device is also not considered to be an efficient solution. Accordingly, single-electronic logic devices have heretofore been considered to be impractical due to their sensitivity to random background charge effects, and the consequent instability of the device's logic state.
Accordingly, what is needed in the art is a single-electron device and method of manufacturing thereof that overcomes the above-mentioned problems, and in particular minimizes random background charge effects on device function.